Coextrusion feedblocks are used for bringing together molten streams of thermoplastic materials from multiple extruders. The individual streams from different extruders are brought together in the coextrusion feedblock to form particular multi-layer arrangements. The resulting multi-layer extrudate flow is then delivered to a subsequent extrusion die, or another downstream tool, to produce the desired composite coextrusion structure.
In the process of bringing together multiple streams of different plastic materials, the different materials commonly have different properties. For example, different plastics tend to exhibit different viscosities. The variations in viscosity or other properties can adversely impact the layer uniformity of the resulting multi-layer coextrusion structure. To compensate for this, it is sometimes desirable to adjust the profile of one or more of the channels through which the different streams pass. In the past, this has been attempted by using certain types of profiling systems.
Existing profiling systems have not been ideal for all applications, have had particular limitations, and could be improved in several ways. For example, the impact and/or adjustment capabilities of existing profiling components on coextrusion flow channels are limited. In addition, conventional profiling systems only have adjustability for the coextrusion flow channels. Further, some profiling systems require off-line tuning for all profile adjustment assemblies, meaning extrusion must be stopped and every profiling component removed and profiled by machining and polishing. Still further, some known profiling components are limited in terms of the types of adjustment assemblies they can affect. Further yet, many conventional coextrusion feedblocks are limited in terms of their ability to control distortion when delivering extrudate from the feedblock into a die, which involves the extrudate spreading into the final film, sheet, or coating.
It would be desirable to provide a coextrusion feedblock that has one or more profiling components for one or more coextrusion channels. It would be particularly desirable to provide one or such more profiling components that can be adjusted in situ (i.e., while in the feedblock, without having to remove such component(s) from the feedblock). It would also be particularly desirable to provide a profiling system that is configured to make both course and fine adjustment assemblies for one or more coextrusion channels.
Further, in some cases, it would be desirable to provide a coextrusion feedblock that has one or more profiling components for the main (or “central”) flow channel, as well as profiling components for one or more coextrusion channels. Still further, it would be desirable to provide a combination of profiling components (e.g., for one or more coextrusion channels, and optionally also for the main flow channel) that can provide an adjustment impact and a range of adjustment iterations that are better than conventional profiling systems. Finally, in some cases, it would be desirable to provide a coextrusion feedblock that is configured to minimize distortion during delivery of extrudate from the feedblock into a die, and during the resulting spreading of the extrudate into the final film, sheet, or coating.